1. Field of the Invention
The invention relates to a digital data recording/reproduction apparatus and, more particularly, to a digital data recording/reproduction apparatus for recording/reproducing data onto and from an optical recording medium in the form corresponding to a compact disc for music, for example.
2. Description of the Prior Art
A compact disc in which an audio signal is digitized and optically recorded is well known. The compact disc is a recording medium having a diameter of 12 cm and capable of recording data equal to or greater than about 500 megabytes, for example. As a result, this compact disc can be employed as a digital-data recording medium for recording a large amount of data.
A CD-ROM has been standardized in which digital data other than audio data can be recorded in the music recording area. In the CD-ROM, digital data is recorded in the same manner as the music compact disc. An optical disc with a diameter of 12 cm is employed on which tracks are formed in a spiral fashion, similarly to the music compact disc. The recording data is doubly encoded with CIRC (Cross Interleave Reed-Solomon Code), EFM modulated (8-14 modulation) and optically recorded on the optical disc.
In such a CD-ROM, one sector (one block) that is a unit for data recording is composed of one subcode block of 98 frames. In other words, in the music compact disc, an 8-bit subcode of P.about.W per frame (R.about.W are also called "users' bits") is prepared. Since the subcode provides one information unit (address) with 98 frames, the 98 frames are called a "block."
Basically, the CD-ROM is a recording medium for read-out only. The CD-ROM has a large memory capacity, enables a large amount of copies and provides information with less deterioration. Utilizing such features, the CD-ROM is used for the recording of data of various kinds of dictionaries or data of research materials.
In recent years, an additional recording type optical recording medium, i.e. an optical magnetic disc, for enabling erasure and rerecording has been developed. It has been proposed to use such an optical magnetic disc to record and reproduce digital data. Additional data can be recorded or rerecorded on such a compact disc (hereunder called "CD-WO" for compact disc, write once) or the data can be erased and rerecorded (hereunder called a "CD-erasable"). Thus its extensive application in various fields can be expected as compared with a CD-ROM which allows reproduction only.
In the CD-WO or CD-erasable, it is useful if the writing/rewriting of data can be done in a unit of one sector. In contrast, the music compact disc is for reproduction only and data is reproduced in the order of a time sequence.
In the music compact disc, the data is sequential and an interleave of a maximum of 108 frames is used for the recording data. For this reason, when the CD-WO or CD-erasable is used in the same signal processing manner as the music compact disc, complicated signal processing is needed in the case where the data is to be written into an arbitrary sector or where data of an arbitrary sector is rewritten. If the signal format of the CD-WO or CD-erasable is altered to be quite different from that of the music compact disc so as not to need such complicated processing, the compatibility between the CD-ROM, CD-WO and CD-erasable is lost.
In the compact disc, a CIRC is employed in which an interleave delay is made for symbols of each column on a two-dimensional data array including a developed and added parity of the C.sub.2 sequence using the Reed-Solomon code and in which a parity of the C.sub.1 sequence is developed and added using the Reed-Solomon code. In such a CIRC, an interleave of a maximum of 108 frames is applied and convolution encoding is made so that an optimization for sequential data such as music data can be achieved. On the other hand, one sector is composed of a subcode block of 98 frames, which is a unit for data writing and read-out in a CD-WO or CD-erasable.
Consequently, when the rewriting of data of an arbitrary sector is done, its influence extends to two sectors before the sector and two sectors after the sector. Namely, if the data of the arbitrary sector is rewritten, the parity of the C.sub.1 sequence relating to data of the two sectors before the sector and data of the two sectors after the sector tends to vary.
For this reason, in the case of the rewriting of data into an arbitrary sector, there is a need to take in data of that sector and two sectors lying after and before the sector respectively and to correct the data after obtaining the parity of the C.sub.1 sequence.
Therefore, as proposed in the specification of U.S. patent application Ser. No. 250,515, filed Sept. 29, 1988, for instance, at least two continuous sectors with all [0] data are inserted between sectors for data recording, and it is proposed that only every third sector is used as a sector for data recording, for example. While with this scheme there is no need to obtain the parity of the adjacent sectors, the data recording capacity is eventually deteriorated to about 1/3 at worst.